Circuit breaker sickle shaped contact actuating mechanism



April 1957 P. L. TAYLOR m m. 2,789,185

CIRCUIT BREAKER SICKLE SHAPED CONTACT ACTUATING MECHANISM Filed Nov. 3, 1953 2 Sheets-Sheet 2 United States Patent CIRCUIT BREAKER SICKLE SHAPED CONTACT ACTUATING MECHANISM Philip L. Taylor, deceased, late of Abington, Mass, by Dorothy S. Taylor, administratrix, Abington, Mass, and Joseph M. Ramrath, Mattapan, Mass, assignors to Allis-Chalmers Manufacturing Company, Milwaukee, Wis., a corporation of Delaware Application November 3, 1953, Serial No. 389,952

' 4 Claims. (Cl. 200-150) This invention relates to electric circuit interrupters and more particularly to are extinguishing structures therefor.

More specifically this invention relates to a novel structure for efiecting the very rapid initiation, elongation and extinction of electric arcs drawn in circuit interrupters. This invention is applicable to the interruption of high voltage arcs such as those drawn in 287 kv. circuit but is also applicable on low voltage circuits.

Experience has demonstrated that a rapid lowering of the dielectric strength of an arc extinguishing fluid, such as oil, occurs after it impinges upon the arc stream. It is therefore desirable to eliminate such contaminated fluid as quickly as possible, and to subject the arc stream to the action of fresh fluid of high dielectric strength. The isolation or disconnection of a capacitance load by a circuit breaker in an alternating current system is subject to transient overvoltages, the magnitudes of which depend on the capacitance of the load, the voltage of the system, and the type of the circuit breaker. In isolating such a capacitance load, interruption at the first current zero in the arc of the leading current is readily effected at a relatively small contact separation. In one-half cycle after the first current zero, the voltage of the source has reversed to its crest value, and approximately double this voltage appears across the circuit breaker contacts as a circuit recovery voltage. Whether or not restriking of the arc occurs depends on several factors, such as the type of the circuit breaker, includiug the speed and the magnitude of the separation of its contacts, the magnitude of the circuit recovery voltage, and the leading kv. a. of the load.

These circuit conditions are diflicult if not impossible to control. Therefore, restriking in most breakers must be expected especially under severe operating conditions, and the circuit interrupting structures must operate efliciently under such conditions.

In accordance with this invention, a new and improved circuit interrupting structure is provided in which an arc interrupter is immersed in arc extinguishing fluid. The interrupter may comprise a pressure generating chamber, a pair of cooperating contacts arranged in the chamber and comprising a stationary arcing contact and a movable sickle shaped contact member, and an insulating stud or push rod supported in and protruding through the chamber. The sickle shaped contact member is pivotally mounted between its ends with one end thereof supporting a movable arcing contact and the other end being connected to a pair of drag links. The insulating push rod is guided for reciprocal longitudinal motion. A metallic cap is secured to one end of the push rod and is slotted to form a bifurcated portion. The other end of the drag links are pivotally connected to the metallic cap within the slot formed by the bifurcated portion. The push rod is provided for actuating the sickle shaped member and movable arcing contact in contact closing direction against a biasing means which is provided for actuating the sickle shaped member and movable arcing contact in contact opening direction. Upon movement of the push rod in contact opening direction, the sickle shaped member and the movable arcing contact are actuated to contact opened position by their biasing means to separate the arcing contacts. A piston may be arranged to operate at the same time or arranged to operate in a predetermined sequence with the movable contact and to force a flow of fluid under pressure adjacent the arcing contacts to extinguish the are drawn therebetween, the movable contact being actuated independently of the movement of the piston.

It is, therefore, one object of the present invention to provide a new and improved circuit breaker mechanism for establishing and lengthening an arc. I

Another object of this invention is to provide a new and improved circuit interrupting mechanism for estab lishing and lengthening an arc in a jet of fluid in which the contacts are opened independently of the movement of the piston of the fluid pump.

A further object of this invention is to provide a new and improved arcing contact structure in which the configuration of the contact actuating mechanism aids are extinguishment.

A still further object of this invention is to provide a contact actuating mechanism which is small and compact.

Objects and advantages other than those set forth will be apparent from the following description when read in connection with the accompanying drawings, in which:

Fig. 1 is an elevational view partly in section of a circuit interrupter embodying the invention and shown in circuit closed position;

Fig. 2 is an enlarged sectional view through one of the interrupting devices shown in Fig. 1;

Fig. 3 is a side view partly in section of the contact actuating mechanism shown in Fig. 2; and

Fig. 4 is a cross sectional view taken along the line IV-IV of Fig. 2.

Referring to the drawing by characters of reference, Fig. 1 illustrates an oil circuit breaker unit of the high voltage type such as that used in power transmission systems. Unit 1 is suspended from one line terminal of the circuit interrupter in a suitable tank 2 and submerged in a suitable insulating arc extinguishing fluid, such as oil. A conducting bridging bar 3 serves to connect electrically the arc extinguishing unit 1 with an identical unit 4 in a manner well known in the art. Supported on a cover 5 of the tank 2 are a pair of terminal bushings 6 and 7 (partially shown) to the lower ends of which are secured arc extinguishing units 1 and 4. The cross bar 3 is actuated reciprocally in the vertical direction by an insulating lift rod 8 to open and close the contacts of the arc extinguishing units 1 and 4.

Fig. 2 is an enlarged view in cross section of the left hand arc extinguishing structure shown in Fig. l. The right hand arc extinguishing structure is of similar design. In Fig. 2 the interrupting chamber 9 contains interrupting and pressure generating arcing contacts 10, 11 and 12, of which the movable contact 10 is mounted at one end of a sickle shaped member 13 pivotally mounted at a point 14 between the ends thereof. Point 14 is arranged above contact 11.

As shown in Fig. 2, the stationary contact structure 11 comprises a plurality of arcuate segments usually four in number biased together by spring means (not shown) to provide a loose pivotal mounting for each segment. The upper end of each segment of contact structure 11 is grooved to form a rectangular recess or slot 17 extending into structure 11 from the top end thereof transversely of the longitudinal axis of structure 11. The lower'end of each segment forming contact structure 11 is grooved to form a cylindrical recess or slot 18 extending into structure 11 from the lower end thereof substantially parallel with orcoaxially with structure 11. The slot walls 19 and 20 of slots 17 and 18, respectively, form contact surfaces which engage contacts and 12 when in contact closed position.

A perforated insulating plate 24 servesas the lower mounting for the contact structure 11. An insulating tube 25 holds an impulse grid structure 42 and the tulip shaped contact structure 11 in coaxial relationship in the interrupting chamber 9. Frame means 21 are providedfo'r independently mounting the arcuate segments for limited freedom of movement. Each segment may be so disposed that when the breaker is moved into contact closed position the contact surfaces 19 and 20 of the slots 17 and 18, respectively, engage the opposing contact surfaces of the contacts 10 and 12 with a wiping action. V a

If'the contacts 10 and 12 move slightly out of their usual path, the arcuate segments will still move into engagement with contacts 10 and 12 to provide a tight electrical connection. Contacts 10, 11 and 12 are separated upon the downward movement of an insulating stud or push rod 26 guided for reciprocal longitudinal motion. Springs 27 bias member 13 in contact opening direction so that upon the downward movement of push rod 26 and of bridging contact 3 and operating rod 8 in contact opening direction the springs rapidly accelerate sickle shaped member 13 and interrupting arcing contact 10 in contact opening direction.

The sickle shaped member 13 is attached at 28 to a pair of drag links 29. Links 29 are pivotally mounted by pin 30 on a metallic cap 32 secured to insulating push rod 26. Thernetallic cap 32 may be slotted 'to form a bifurcated portion and links 29 and sickle shaped member 13 are arranged in the slot.

The push rod 26 itself may be provided to form the bifurcated portion if the push rod is made of insulating material strong enough to stand the strain of circuit breaker operation. The upper end of springs 27 rest against a fixed shoulder 31 of the frame structure of the interrupting chamber 9. The circuit" breaker structure shown in Fig. 2 may employ spring actuated interrupting contacts such as contacts 10, 11, alone or 'in combination with spring actuated oil pumps for the interruption of line charging currents and such low value of inductive currents as are not efi'ectively interrupted by suicidal type devices.

Push rod 26 at its end remote from the cross bar 3 abuts against a push rod 34. Push rod 34 is provided with a valve stem 35 and a spring biased valve element 36 forming a part of a spring biased piston 37. Piston 37 is arranged in a cylinder 38 of a pump 39. Cylinder 38 is open at its lower end so that oil ahead of piston 37 will be forced through the lower open end of cylinder 38 into the pressure or interrupting chamber 9.

During a circuit closing operation of the interrupter, the cross bar 3 forces the push rod 26 upward. Push rod 26 in its upward movement rotates sickle shaped member 13 and arcing contact '10 counterclockwise to cause'contact 10 to engage the slot wall sides of its fixed contact structure 11. Push rod 26 in its upward movement to closed circuit position pushes rod 34 upward against the biasing action of the spring biased piston 37. The electrical circuit through this are interrupting chamber 9 comprises alead-in conductor (not shown) arranged in the bushing 6, the support and the Walls of chamber 9, flexible connector 41, sickle shaped member 13, movable interrupting arcing contact 10, fixed interrupting arcing contact 11, movable arcing contact 12,

and cross bar 3.

plates which form part of the walls of the paths through which the arcs produced by contacts 14 11 and 12 are drawn.

Each interrupting unit is provided with two parallel cylindrical resistor assemblies 45. The upper end of each resistor assembly 45 is conductively connected to an electrostatic shield 46. Shield 46 is conductively connected to housing 44 which in turn is conductively connected to the lower terminal end of the breaker bushing 6. The lower end of each resistor assembly 45 is conductively connected to the lower electrostatic shield 47. Shield 47 is conductively connected to an arcing electrode comprising a disk like member 48 through a conductive circuit comprising bolts 49, plate 50, bolts 51 and ring support 52.

The lower end of unit 1 is provided with an insulating nozzle 55 forming a fluid opening 56. The arcing electrode 48 is secured within unit 1 between the lower end of the barrier plate assembly 43 and the blast opening 56.

When it is desired to open the electric circuit passing through the interrupter, or when overload conditions exist in the electric circuit controlled by the interrupter, suitable operating mechanism (not shown) moves the insu-lating lift rod 8 to result in a downward movement of the conducting cross bar 3 and the movable contacts 12, 12.

The downward movement of cross bar 3 causes insulating operating rod 26 to rotate sickle shaped member 13 and contact 10 clockwise about the pivot stud 14 to draw an are between contacts 10 and 11. Substantially simultaneously therewith or with a slight delay, the movable bayonet shaped contact 12 separates from the intermediate or fixed contact 11 to draw an are between contacts 11 and 12. The downward movement of operating rod 26 causes the downward movement of piston 37 to move the oil within the pump cylinder 38. The oil, now under pressure within the pump cylinder 38, flows under pressure out of the cylinder 38, chamber 9 and through the barrier plate stack 42 transversely of the substantially longitudinal axis of the arc extinguishing unit 1.

If it is desirable to isolate the oil and gas from between barrier plate assemblies 42 and 43, the oil and gas passing through barrier plate stack 42 is exhausted through a chamber 57 and exhaust port 58 to the inside of tank 2. As shown in Fig. 2, the port 58 is closed with a pipe plug 59 so that the oil and gas flow through assembly 42 will pass through assembly 43. Assembly 42 is arranged to direct the oil under pressure from the cylinder 38 transversely of the longitudinal axis of the arc extinguishing action and through exhaust ports (not shown) into the arc extinguishing barrier plate assembly 43.

The grid assembly 42 is particularly useful in circuit breakers used to isolate a capacitive load of such capacitance and voltage that the voltage gradient across the arc interrupting contacts of the circuit breaker exceeds the dielectric strength between these contacts.

During the interruption of low currents, the operating rod 26 moves downwardly at the same speed as the cross bar 3 to result in the sickle shaped member 13 and contact 10 rotating clockwise about stud 14 to draw an are between contacts 10 and 11. The rod 34 and piston 37 follow the downward movement of operating rod 26. Valve element 36 closes and moves the oil in cylinder 38 into interrupting chamber 9. This action occurs during the interruption of low currents.

During the interruption of high current arc-s, the pressure created by the are drawn between contacts 10 and 11 may prevent the downward movement of the piston 37 and this, in turn, halts the downward movement of the rod 34. Push rod 34 then separates from rod 26 at surface 33 on push rod 34.

When the pressure subsides within the barrier plate assembly 42 oil under pressure within chamber 9 flows out through barrier plate assembly 42 to flush the region where the are occurred between contacts and 11. This scavenging action raises the dielectric strength of the oil in the barrier plate assembly 42 and prevents restriking between contacts 10 and 11 which would prolong the arcing time of the interrupter. It also prevents premature breakdown of the contact gap during and immediately following closing operation. The grid assembly 42 is particularly useful in circuit breakers used to isolate a a capacitive load of such capacitance and voltage that the voltage gradient across the arc interrupting contacts of the circuit breaker exceeds the dielectric strength between these contacts.

The downward movement of contact '12 draws an arc in the barrier plate stack assembly 43 between contact 12 and the fixed contact 11. The arc drawn between contacts 11 and 12 breaks down a portion of the arc extinguishing liquid which surrounds the arc and saturates the barrier plate assembly 43. The barrier plate assembly 43 may be of the type shown and claimed in U. S. Patent No. 2,467,542, Philip L. Taylor, April 19, 1949. This type of barrier plate assembly provides helical passages which produce a helical flow of liquid through the barrier plates and a contact passageway 60 formed there- 1n.

The flow of oil under pressure through barrier plate assembly 42 is directed around the intermediate contact structure 11 and into the contact passageway 60 where it is acted upon by the barrier plate assembly 43 to produce the helical liquid flow to extinguish the interrupting are established in barrier plate assembly 43.

While the circuit breaker is opening, an arcing surface 61 of the movable contact 12 passes the arcing electrode 48 before passing through nozzle 55. Part of contact 12 moves through the nozzle during interruption of the power arc. Immediately after momentary interruption at a current zero, the returning voltage between contacts 10, 11 and 11, 12 causes current to flow through the resistor assembly 45 because the voltage breaks down the gap at one or more points on the surface of arcing electrode 48 (due to the short gap between the electrode 48 and the body of contact 12 as compared with the main interrupting gap between surfaces 61 and contact 11 and contacts 10, 11). The resistor assembly 45 is thereby inserted in series with the power circuit through an auxiliary are so that the resistance circuit now shunts the contacts 10, 11 and 12.

The magnitude of the arc current is correspondingly decreased by the resistance and the difliculty of completely interrupting the current is greatly diminished, particularly in the case of circuits having high rates of increase of the recovery voltage and also in the case of capacitance switching. The ohmic value of the resistance 45 depends on the characteristics of the circuit to be controlled.

When the comparatively weak arc current through the resistor is finally extinguished by the cooling eflect of the oil, further downward movement of contact 12 serves to increase the oil gap for isolating the contacts from each other so that there is no danger of flashover or restriking of the arc.

Thus, an eificient, simple and compact interrupting unit is provided that occupies less space within the oil tank than conventional interrupting chambers and that is easy to inspect or repair. The resistor unit can be readily removed from the breaker and replaced independently of the chamber and the contacts therein so that complete disassembly of the chamber construction is unnecessary.

Although but one embodiment of the present invention has been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. In a circuit interrupter, means for establishing and lengthening an arc comprising a sickle shaped member pivotally mounted at a point between the ends thereof, a pair of arcing contacts comprising a movable contact mounted at one end of said member, a link connected at one end to the other end of said member, a cylinder containing an arc extinguishing fluid, a piston arranged in said cylinder, a push rod guided for reciprocal longitudinal motion, means for detachably connecting said push rod to said piston, means for pivotally connecting said push rod to the other end of said link, means for actuating said push rod in one direction to move said piston and said member in contact closed position, and means for actuating said push rod in another direction to disconnect said push rod and said member from said piston and to move said member in contact opening direction to separate said arcing contacts and to cause said piston to force fluid under pressure adjacent said arcing contacts to extinguish the arc.

2. In a circuit interrupter, means for establishing and lengthening an arc comprising a sickle shaped member pivotally mounted at a point between the ends thereof, a pair of arcing contacts comprising a movable contact mounted at one end of said member, a link connected at one end to the other end of said member, a cylinder containing an arc extinguishing fluid, a piston arranged in said cylinder, a push rod guided for reciprocal longitudinal motion and slotted at one end thereof to form a bifurcated portion, means for detachably connecting said push rod to said piston, means for pivotally connecting the other end of said link Within the bifurcated portion of said push rod, means for actuating said push rod in one direction to move said piston and said member to contact closed position, and means for actuating said push rod in another direction to disconnect said push rod and said member from said piston and to move said member in contact opening direction to separate said arcing contacts and to cause said piston to force fluid under pressure adjacent said arcing contacts to extinguish the arc.

3. In a circuit interrupter, means for establishing and lengthening an arc comprising a sickle shaped member pivotally mounted at a point between the ends thereof, a pair of arcing contacts comprising a movable contact mounted at one end of said member, a link connected at one end to the other end of said member, a cylinder containing an arc extinguishing fluid, a piston arranged in said cylinder, a push rod guided for reciprocal longitudinal motion, a metallic cap secured to one end of said push rod and slotted to form a bifurcated portion, means for pivotally connecting the other end of said link within the bifurcated portion of said metallic cap, means for detachably connecting said push rod and said metallic cap to said piston, means for actuating said push rod in one direction to move said piston and said member in contact closed position, and means for actuating said push rod in another direction to disconnect said push rod and said member from said piston and to move said memher in contact opening direction to separate said arcing contacts and to cause said piston to force fluid under pressure adjacent said arcing contacts to extinguish the are.

4. In a circuit interrupter, means for establishing and len thening an arc comprising a sickle shaped member pivotally mounted at a point between the ends thereof, a pair of arcing contacts comprising a movable contact mounted at one end of said member, a pair of drag links connected at one end to the other end of said member, a cylinder containing an arc extinguishing fluid, a piston arranged in said cylinder, an insulating push rod guided for reciprocal longitudinal motion, a metallic cap secured to one end of said push rod and slotted to form a bifurcated portion, means for pivotally connecting the other end of said pair of drag links within the bifurcated por- References Cited in the file of this patent UNITED STATES PATENTS Baker et a1. j Nov. 23,

Cushing Mar. 8,

FOREIGN PATENTS Great Britain Q May 30,

Germany n Apr. 2,

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